Ankylosaurus (centre) and T-Rex (right), illustration. The T. rex or colloquially T-Rex, it was one of the most well-represented of the large theropods. It was a huge carnivore and primarily ate herbivorous dinosaurs, including Triceratops. Tyrannosaurus rex may not have been a lone operator and may have hunted in packs. It lived 68 million years ago during the Cretaceous Period throughout what is now western North America. Ankylosaurus dinosaur lived in the early Mesozoic era, in the Jurassic and Cretaceous periods, between about 125 and 65 million years ago. It was a herbivorous dinosaur, and the spiked armour served as protection against carnivorous dinosaurs. Ankylosaurs also possessed a heavy club-like tail, which could be swung at attackers to injure their legs. A full-grown adult could be 6 to 9 metres long, weighing over 6 tonnes.